Update version of CodePlex/PHPExcel in composer.json

>=1.7 instead of 1.7.8
CodePlex/PHPExcel → phpoffice/phpexcel in composer.json

CodePlex/PHPExcel → phpoffice/phpexcel
Merge pull request #41 from kachkaev/patch-1

Update version of CodePlex/PHPExcel in composer.json